Micromechanics of semicrystalline polymers: Yield kinetics and long-term failure

The process of plastic deformation in semicrystalline polymers is complicated due to the operation of a variety of mechanisms at different levels and is strongly dependent on their underlying microstructure. The objective of this work is to establish a quantitative relation between the microstructure and the mechanical performance of semicrystalline polymers, as characterized by elasto-viscoplastic deformation. To do that, a micromechanically based constitutive model is used. The model describes the material as an aggregate of two-phase layered composite inclusions, consisting of crystalline lamellae and amorphous layers. The starting point for adding quantitative abilities to the model, in particular for the yield kinetics, is formed by experimental observations on both the yield kinetics and the time-to-failure of polyethylene at different temperatures, which reveal the contribution of two relaxation processes. To predict the thermo-rheologically complex short-term and long-term failure behavior, the crystallographic slip kinetics and the amorphous yield kinetics are re-evaluated, and the Eyring flow rule is modified by adding a temperature shift function. To enable the prediction of both tension and compression, a non-Schmid effect is added to the constitutive relation of each slip system. The creep behavior of polyethylene is then simulated directly using the multiscale, micromechanical model, predicting the time-to-failure, controlled by plastic deformation. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012